Insect repellent compositions

ABSTRACT

Liquefiable powder compositions are disclosed for the delivery of topical insect repellents. In particular, microporous cellulosic powders, such as cellulose acetates or nitrates, are disclosed as high liquid content vehicles for the delivery of liquid insect or tick repellent preparations. The resulting powders permit the application of the arthropod repellent preparation by simply rubbing or brushing the formulation onto the skin, in such a manner that the powder liquefies and appears to vanish. Upon application, the frangible, liquid loaded cellulosic powders break up into minute particles that do not pass easily beyond the initial layers of the skin, but do permit the slow release of the insect repellent agent.

REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 619,721, nowabandoned, which was a continuation-in-part of U.S. Serial No. 358,690filed May 30, 1989, now U.S. Pat. No. 5,000,947.

BACKGROUND OF THE INVENTION

The technical field of this invention is the topical application ofpersonal care agents and, in particular, methods and compositions fortopical application of agents to repel insects and other arthropods.

In recent years the public has become increasingly aware that the bitesof insects and arachnids is not only a severe nuisance in certainseasons and regions, it can also carry a life-threatening risk ofinfection with such illnesses as Lyme disease and equine encephalitis.(The term "insect" is used herein to encompass insects, ticks, arachnidsand other nuisance or harmful arthropods, generally.)

One of the most effective first lines of defense against such bites, andone which causes little stress to environmentally beneficial arthropods,is the use of chemical repellents. A variety of repellents of diverseeffectiveness have been used over the years, including such materials ascitronella; safe and effective repellents in current use includeN,N-diethyl-m-toluamide (DEET) and 2-ethyl-1,3-hexanediol (6-12)

Compositions useful as insect repellents should disperse easily onto theskin, adhere closely to the skin, resist penetration through the skin,and resist shedding with perspiration or rain. Unfortunately most insectrepellents do not fully satisfy these requirements in terms ofdurability and prolonged residence on the skin. For example, DEET, usedalone or compounded with common cosmetic extenders, gradually penetratesinto deep layers of the skin where its insect-repelling activity isreduced.

There exists a need for better insect repellent compositions for moreeconomical and reliable protection against the distress and danger ofinsect bites, tick bites and the bites of other arthropods.

SUMMARY OF THE INVENTION

Liquefiable polymer powder compositions are disclosed for the deliveryof topical insect repellents In particular, microporous cellulosicpowders, such as cellulose acetates or nitrates, are disclosed as highliquid content vehicles for the delivery of liquid insect and tickrepellents to the skin. The resulting powders permit the application ofan arthropod repellent preparation by simply rubbing or otherwiseapplying the formulation to the skin in such a manner than the powderliquefies and appears to vanish. Upon application the frangible,liquid-loaded cellulosic powder particles break up into minute fragmentswhich do not pass beyond the superficial layers of the skin, but whichdo permit slow release of the repellent agent.

Details of the formation of cellulosic powders can be found in theabove-referenced parent application, U.S. Ser. No. 358,690, filed May30, 1989, U.S. Pat. No. 5,000,947 and a commonly-owned, copendingapplication entitled "Process For Producing Liquid-Loaded Powders", byLarry D. Nichols and John F. Cline, filed contemporaneously herewith,both of which are incorporated herein by reference. A preferred polymerliquid-loadable powder includes microporous cellulose triacetateprepared by the method of the above application, entitled "Process ForProducing Liquid-Loaded Powders".

In one technique, the liquefiable powders are formed by dissolving acellulosic polymer and a pore-forming liquid in a volatile, polarsolvent (e.g., a low molecular weight halogenated hydrocarbon, ester ordiester) and then dispersively evaporating the solution, for example, byspray drying. Suitable volatile solvents for cellulosic polymers includemethylene chloride, acetone, ethyl acetate, ethyl carbonate, methylformate and the like. Methylene chloride is a preferred solvent when thecellulosic polymer is cellulose triacetate. Alternatively, othersolvents, such as formic acid or the like, can be used and the resultingsolution can be sprayed into a non-solvent such as methanol where thepowder particles are then recovered by filtration and rinsing. Theactive agent can be incorporated into the solvent or introduced byliquid phase substitution after the powder is formed.

The cellulosic powders useful in the present invention can range fromabout one to about 500 microns in average diameter, preferably fromabout 5 to about 100 microns in average diameter, and typically areroughly microspherical in shape. They are further characterized by beingmicroporous with interconnecting pores ranging in size from about one toabout 500 nanometers and are capable of holding liquid payloads ofactive agents.

The cellulosic powder can be formed from cellulosic polymers chosen fromthe group of cellulose acetates, cellulose butyrates, cellulosenitrates, cellulose propionates, ethyl celluloses and discrete ormolecular mixtures thereof. One preferred cellulosic powder is apolymeric powder of cellulose triacetate, having a (dry) acetyl contentgreater than about 42 percent. The liquid content of the cellulosicpowders of the present invention can range from about 50 percent toabout 95 percent by weight.

Compositions made in accordance with the present invention permit thedelivery of effective amounts of active arthropod repellent ingredientwithout many of the problems normally associated with unconfined liquidsand oils. By assisting in the distribution of repellent agents uniformlyover the skin, and retarding the loss of such agents into the skin oroff of the skin into the environment, the compositions of the inventionenhance efficacy, improve economy and reduce the risk of adverse humanor environmental reactions.

Arthropod repellents which can be used in the practice of the inventioninclude N,N-diethyl-m-toluamide (DEET) and 2-ethyl-1,3-hexanediol (6-12)and derivatives or mixtures thereof, as well as other repellents knownnow or in the future to those skilled in the art. Liquid formulationscontaining 6-12 in a cellulosic liquefiable powder can be 100% active,or can contain extenders, emollients or diluents such as mineral oils,silicone oils, or fatty esters or alcohols Liquid formulationscontaining DEET in a liquefiable cellulosic powder can generally not be100% active, since pure DEET is a powerful solvent and softening agentfor many polymers, including cellulose esters and nitrates. Formulationscontaining as much as 65% DEET in inert liquids such as fatty esters andalcohols are acceptable and well tolerated by the polymer matrix.

In one embodiment the repellent agent can be incorporated into frangiblecellulosic microbeads or other powder forms, and then formulated into acream or lotion type vehicle by mixture with a liquid base.Alternatively the compositions can be formulated as loose powders,compacted into cakes, blended into binders and shaped into bars orapplication sticks.

Suitable liquid bases for cream or lotion type embodiments includewater, mineral or silicone oils, volatile silicones, and moisturizingagents such as glycerin or propylene glycol.

Regardless of the embodiment, various additives can be mixed togetherwith the liquid loaded microcapsules (or liquid base) including, forexample, talc, cornstarch, waxes, silicones, analgesics, cosmetics,fragrances, lubricants, emollients, moisturizers, medications and otherpersonal care agents, colorants, pearlescent agents, and mixtures ofsuch additives.

In the compacted cake embodiments, the liquid loaded powders can becompacted to packing densities ranging from about 55 percent to about 75percent, more preferably from about 60 percent to about 70 percent ofthe void-free density of the combined materials to yield cakes that aredry and firm and yet readily permit transfer of the formulation to theskin by finger or brush.

Such compacted cakes can be obtained by applying a pressure ranging fromabout 50 to about 80 PSI to a cellulosic powder which has beenappropriately loaded with a liquid payload of the active agent. In theabsence of other additives, the resulting shaped articles have acompacted density ranging from about 0.55 to about 0.75 gm/cc.

Sticks or bars incorporating liquefiable powders with active agentpayloads can be made by a variety of techniques. For example, sticks canbe formulated by compounding a liquefiable powder with fatty alcohols,fatty acids, and/or salts of fatty acid anions with metallic oralkanolamine cations to produce a stick having a soap as the bindingagent.

Alternatively, stick compositions can be formed by compounding aliquefiable powder with soft water-soluble polymers, such aspolyethylene glycols or polypropylene glycols, to produce a stick havinga soluble wax as the binding agent. Sticks can also be made up bycompounding a liquefiable powder with silicones or with blends ofliquids and solids, such micronized aluminum antiperspirant salts and/orpropylene glycols, to produce sticks having a thick or partiallysolidified slurry as the binding agent In yet another approach, stickscan be formed by compounding a liquefiable powder with a fusible wax,such as myristyl myristate, and then applying heat and pressure toproduce sticks having a fatty ester wax as the binding agent.

The above binding agents can be introduced directly, or as payload in asecond portion of liquefiable powder to be blended with that carryingthe active ingredient. Other methods of stick production will readilyoccur to those skilled in the art.

The invention will next be described in connection with certainexemplary methods and compositions. However, it should be clear thatvarious additions, subtractions and changes can be made by those skilledin the art without departing from the spirit or scope of the invention.For example, although the illustrative examples describe the use of DEETand 6-12 as the active agents, various other insect repellents can bedissolved or dispersed within the liquid phase of the cellulosic powderto provide similar insect repellent action.

In some applications, it may also be preferable to include a quantity ofa dry cellulosic powder (e.g., less than 50 percent of the totalcellulosic components) to provide additional structural integrity to thecomposition. The term "dry cellulosic powder" is used herein to describepowders whose internal pores are liquid-free or have a liquid content ofless than 50 percent.

DETAILED DESCRIPTION

The examples below illustrate the preparation of liquefiable arthropodrepellent loaded powders.

EXAMPLE 1

A liquefiable powder was prepared by spray evaporative drying. A liquidporogen was prepared from 60 parts by weight of N,N-diethyl-m-toluamide(DEET) and 40 parts by weight of 2-octyldodecanol, a heavy secondaryalcohol commonly used in cosmetic formulations. 40 grams of cellulosetriacetate was dissolved in 3000 gm of methylene chloride by moderatestirring for 4 hours. To that solution was added 460 gm of thepreviously prepared porogen diluted with 1000 gm of methylene chloride.The resulting homogeneous solution was sprayed at 1000 PSI from a0.0135" nozzle, downward into a tower 100 cm in diameter and 300 cmtall, through which 1250 liters per minute of solvent-free air waspassing from top to bottom.

The evaporatively-formed powder was collected on a fabric filterspanning the bottom of the tower, and the solvent-laden air was passedthrough carbon beds to collect and recover solvent. The product wastransferred to a steel tray and exposed as a 1 cm deep layer in aventilated hood for 25 minutes to remove residual solvent. Analysisshowed 8% cellulose triacetate, 36.8% octyldodecanol, and 55.2% DEET,with less than 5 ppm or residual methylene chloride.

The resulting white powder could be readily dusted onto the skin andmade to liquefy and vanish by gentle rubbing. There was no perceptiblegrit or gumminess.

EXAMPLE 2

A powder like that of example 1 was prepared using as a porogen pure2-ethyl-1,3-hexanediol (6-12) insect repellent. The powder analyzed tocontain 8.1% cellulose acetate and 91.9% 6-12 liquid, with less than 1ppm of methylene chloride.

It will be understood that the above description pertains to onlyseveral embodiments of the present invention. That is, the descriptionis provided by way of illustration and not by way of limitation. Theinvention, therefore, is to be defined according to the followingclaims.

What I claim is:
 1. An insect repellent composition for the delivery ofa topical insect repellent, the composition comprising a formulation ofa frangible, liquid-containing, cellulosic powder formed by sprayevaporation and having particles ranging in average diameter from about1 to about 500 micrometers, the particles further characterized by beingmicroporous with a plurality of interconnecting pores ranging in sizefrom about 1 to about 500 nanometers and having a structure which isreadily fragmented and a liquid insect repellent preparation loadedwithin the pores of the powder particles, such that theliquid-containing powder has a liquid content ranging from about 50percent to about 95 percent by weight, and, upon application andrubbing, the rubbed particles fragment and the insect repellentpreparation is readily released.
 2. The composition of claim 1 whereinthe cellulosic powder is a polymeric powder chosen from the groupconsisting of cellulose acetates, cellulose butyrates, cellulosenitrates, cellulose propionates, ethyl celluloses, and discrete admolecular mixtures thereof.
 3. The composition of claim 1 wherein theliquid insect repellent preparation comprises an insect repellentcompound chosen from the group consisting essentially ofN,N-diethyl-m-toluamide 2-ethyl-1,3- hexanediol, derivatives andmixtures thereof.
 4. The composition of claim 1 wherein the compositionfurther comprises a liquid not incorporated within the frangible powder.